Extrusion-based additive manufacturing of Mg-Zn alloy scaffolds

Porous biodegradable Mg and its alloys are considered to have a great potential to serve as ideal bone substitutes.The recent progress in additive manufacturing(AM) has prompted its application to fabricate Mg scaffolds with geometrically ordered porous structures.Extrusionbased AM,followed by debinding and sintering,has been recently demonstrated as a powerful approach to fabricating such Mg scaffolds,which can avoid some crucial problems encountered when applying powder bed fusion AM techniques.However,such pure Mg scaffolds exhibit a too high rate of in vitro biodegradation.In the present research,alloying through a pre-alloyed Mg-Zn powder was ultilized to enhance the corrosion resistance and mechanical properties of AM geometrically ordered Mg-Zn scaffolds simultaneously.The in vitro biodegradation behavior,mechanical properties,and electrochemical response of the fabricated Mg-Zn scaffolds were evaluated.Moreover,the response of preosteoblasts to these scaffolds was systematically evaluated and compared with their response to pure Mg scaffolds.The Mg-Zn scaffolds with a porosity of 50.3% and strut density of 93.1% were composed of the Mg matrix and MgZn2second phase particles.The in vitro biodegradation rate of the Mg-Zn scaffolds decreased by 81% at day 1,as compared to pure Mg scaffolds.Over 28 days of static immersion in modified simulated body fluid,the corrosion rate of the Mg-Zn scaffolds decreased from 2.3± 0.9 mm/y to 0.7±0.1 mm/y.The yield strength and Young’s modulus of the Mg-Zn scaffolds were about 3 times as high as those of pure Mg scaffolds and remained within the range of those of trabecular bone throughout the biodegradation tests.Indirect culture of MC3T3-E1 preosteoblasts in Mg-Zn extracts indicated favorable cytocompatibility.In direct cell culture,some cells could spread and form filopodia on the surface of the Mg-Zn scaffolds.Overall,this study demonstrates the great potential of the extrusion-based AM Mg-Zn scaffolds to be further developed as biodegradable bone-substituting biomaterials.

Functionalized Hydrogels for Articular Cartilage Tissue Engineering

Articular cartilage(AC)is an avascular and flexible connective tissue located on the bone surface in the diarthrodial joints.AC defects are common in the knees of young and physically active individuals.Because of the lack of suitable tissue-engineered artificial matrices,current therapies for AC defects,espe-cially full-thickness AC defects and osteochondral interfaces,fail to replace or regenerate damaged carti-lage adequately.With rapid research and development advancements in AC tissue engineering(ACTE),functionalized hydrogels have emerged as promising cartilage matrix substitutes because of their favor-able biomechanical properties,water content,swelling ability,cytocompatibility,biodegradability,and lubricating behaviors.They can be rationally designed and conveniently tuned to simulate the extracel-lular matrix of cartilage.This article briefly introduces the composition,structure,and function of AC and its defects,followed by a comprehensive review of the exquisite(bio)design and(bio)fabrication of func-tionalized hydrogels for AC repair.Finally,we summarize the challenges encountered in functionalized hydrogel-based strategies for ACTE both in vivo and in vitro and the future directions for clinical translation.

A novel approach to determine residual stress field during FSW of AZ91 Mg alloy using combined smoothed particle hydrodynamics/neuro-fuzzy computations and ultrasonic testing

The faults in welding design and process every so often yield defective parts during friction stir welding(FSW).The development of numerical approaches including the finite element method(FEM)provides a way to draw a process paradigm before any physical implementation.It is not practical to simulate all possible designs to identify the optimal FSW practice due to the inefficiency associated with concurrent modeling of material flow and heat dissipation throughout the FSW.This study intends to develop a computational workflow based on the mesh-free FEM framework named smoothed particle hydrodynamics(SPH)which was integrated with adaptive neuro-fiizzy inference system(ANFIS)to evaluate the residual stress in the FSW process.An integrated SPH and ANFIS methodology was established and the well-trained ANIS was then used to predict how the FSW process depends on its parameters.To verify the SPH calculation,an itemized FSW case was performed on AZ91 Mg alloy and the induced residual stress was measured by ultrasonic testing.The suggested methodology can efficiently predict the residual stress distribution throughout friction stir welding of AZ91 alloy.

Connexin 43 hemichannels protect bone loss during estrogen deficiency

Estrogen deficiency in postmenopausal women is a major cause of bone loss,resulting in osteopenia,osteoporosis,and a high risk for bone fracture.Connexin 43 (Cx43) hemichannels (HCs) in osteocytes play an important role in osteocyte viability,bone formation,and remodeling.We showed here that estrogen deficiency reduced Cx43 expression and HC function.To determine if functional HCs protect osteocytes and bone loss during estrogen deficiency,we adopted an ovariectomy model in wild-type (WT) and two transgenic Cx43 mice:R76W (dominant-negative mutant inhibiting only gap junction channels) and Cx43 Δ130–136 (dominant-negative mutant compromising both gap junction channels and HCs).The bone mineral density (BMD),bone structure,and histomorphometric changes of cortical and trabecular bones after ovariectomy were investigated.Our results showed that the Δ130–136 transgenic cohort had greatly decreased vertebral trabecular bone mass compared to WT and R76W mice,associated with a significant increase in the number of apoptotic osteocyte and empty lacunae.Moreover,osteoclast surfaces in trabecular and cortical bones were increased after ovariectomy in the R76W and WT mice,respectively,but not in Δ130–136 mice.These data demonstrate that impairment of Cx43 HCs in osteocytes accelerates vertebral trabecular bone loss and increase in osteocyte apoptosis,and further suggest that Cx43 HCs in osteocytes protect trabecular bone against catabolic effects due to estrogen deficiency.

Introducing 3D-potting:a novel production process for artificial membrane lungs with superior blood flow design

Currently,artificial-membrane lungs consist of thousands of hollow fiber membranes where blood flows around the fibers and gas flows inside the fibers,achieving diffusive gas exchange.At both ends of the fibers,the interspaces between the hollow fiber membranes and the plastic housing are filled with glue to separate the gas from the blood phase.During a uniaxial centrifugation process,the glue forms the“potting.”The shape of the cured potting is then determined by the centrifugation process,limiting design possibilities and leading to unfavorable stagnation zones associated with blood clotting.In this study,a new multiaxial centrifugation process was developed,expanding the possible shapes of the potting and allowing for completely new module designs with potentially superior blood flow guidance within the potting margins.Two-phase simulations of the process in conceptual artificial lungs were performed to explore the possibilities of a biaxial centrifugation process and determine suitable parameter sets.A corresponding biaxial centrifugation setup was built to prove feasibility and experimentally validate four conceptual designs,resulting in good agreement with the simulations.In summary,this study shows the feasibility of a multiaxial centrifugation process allowing greater variety in potting shapes,eliminating inefficient stagnation zones and more favorable blood flow conditions in artificial lungs.

Bone tissue engineering via growth factor delivery:from scaffolds to complex matrices

In recent years,bone tissue engineering has emerged as a promising solution to the limitations of current gold standard treatment options for bone related-disorders such as bone grafts.Bone tissue engineering provides a scaffold design that mimics the extracellular matrix,providing an architecture that guides the natural bone regeneration process.During this period,a new generation of bone tissue engineering scaffolds has been designed and characterized that explores the incorporation of signaling molecules in order to enhance cell recruitment and ingress into the scaffold,as well as osteogenic differentiation and angiogenesis,each of which is crucial to successful bone regeneration.Here,we outline and critically analyze key characteristics of successful bone tissue engineering scaffolds.We also explore candidate materials used to fabricate these scaffolds.Different growth factors involved in the highly coordinated process of bone repair are discussed,and the key requirements of a growth factor delivery system are described.Finally,we concentrate on an analysis of scaffold-based growth factor delivery strategies found in the recent literature.In particular,the incorporation of two-phase systems consisting of growth factor-loaded nanoparticles embedded into scaffolds shows great promise,both by providing sustained release over a therapeutically relevant timeframe and the potential to sequentially deliver multiple growth factors.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells(ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue,articular cartilage(AC)has very limited self-repair capacity after traumatic injuries,posing a heavy socioeconomic burden.Common clinical therapies for small-to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies,including microfracture,mosaicplasty,autologous chondrocyte implantation(ACI),and matrix-induced ACI(MACI).However,these treatments frequently result in mechanically inferior fibrocartilage,low cost-effectiveness,donor site morbidity,and short-term durability.It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC.Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments.A deeper understanding of the mechanism of endogenous cartilage healing is furthering the(bio)design and application of these scaffolds.Currently,the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells(ESPCs)presents an evolving improvement for cartilage repair.This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration.Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed.The recent advances in novel(bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs(e.g.adhesion,migration,proliferation,differentiation,matrix production,and remodeling)for cartilage repair are summarized.Finally,this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

In vitro degradation and surface bioactivity of iron-matrix composites containing silicate-based bioceramic

Iron-matrix composites with calcium silicate(CS)bioceramic as the reinforcing phase were fabricated through powder metallurgy processes.The microstructures,mechanical properties,apatite deposition and biodegradation behavior of the Fe-CS composites,as well as cell attachment and proliferation on their surfaces,were characterized.In the range of CS weight percentages selected in this study,the composites possessed compact structures and showed differently decreased bending strengths as compared with pure iron.Immersion tests in simulated body fluid(SBF)revealed substantially enhanced deposition of CaP on the surfaces of the composites as well as enhanced degradation rates as compared with pure iron.In addition,the composite containing 20%CS showed a superior ability to stimulate hBMSCs proliferation when compared to pure iron.Our results suggest that incorporating calcium silicate particles into iron could be an effective approach to developing iron-based biodegradable bone implants with improved biomedical performance.

Addition of heparin binding sites strongly increases the bone forming capabilities of BMP9 in vivo

Bone Morphogenetic proteins(BMPs)like BMP2 and BMP7 have shown great potential in the treatment of severe bone defects.In recent in vitro studies,BMP9 revealed the highest osteogenic potential compared to other BMPs,possibly due to its unique signaling pathways that differs from other osteogenic BMPs.However,in vivo the bone forming capacity of BMP9-adsorbed scaffolds is not superior to BMP2 or BMP7.In silico analysis of the BMP9 protein sequence revealed that BMP9,in contrast to other osteogenic BMPs such as BMP2,completely lacks so-called heparin binding motifs that enable extracellular matrix(ECM)interactions which in general might be essential for the BMPs’osteogenic function.Therefore,we genetically engineered a new BMP9 variant by adding BMP2-derived heparin binding motifs to the N-terminal segment of BMP9′s mature part.The resulting protein(BMP9 HB)showed higher heparin binding affinity than BMP2,similar osteogenic activity in vitro and comparable binding affinities to BMPR-II and ALK1 compared to BMP9.However,remarkable differences were observed when BMP9 HB was adsorbed to collagen scaffolds and implanted subcutaneously in the dorsum of rats,showing a consistent and significant increase in bone volume and density compared to BMP2 and BMP9.Even at 10-fold lower BMP9 HB doses bone tissue formation was observed.This innovative approach of significantly enhancing the osteogenic properties of BMP9 simply by addition of ECM binding motifs,could constitute a valuable replacement to the commonly used BMPs.The possibility to use lower protein doses demonstrates BMP9 HB’s high translational potential.

A culture model to analyze the acute biomaterial-dependent reaction of human primary neutrophils in vitro

Neutrophils play a pivotal role in orchestrating the immune system response to biomaterials,the onset and resolution of chronic inflammation,and macrophage polarization.However,the neutrophil response to biomaterials and the consequent impact on tissue engineering approaches is still scarcely understood.Here,we report an in vitro culture model that comprehensively describes the most important neutrophil functions in the light of tissue repair.We isolated human primary neutrophils from peripheral blood and exposed them to a panel of hard,soft,naturally-and synthetically-derived materials.The overall trend showed increased neutrophil survival on naturally derived constructs,together with higher oxidative burst,decreased myeloperoxidase and neutrophil elastase and decreased cytokine secretion compared to neutrophils on synthetic materials.The culture model is a step to better understand the immune modulation elicited by biomaterials.Further studies are needed to correlate the neutrophil response to tissue healing and to elucidate the mechanism triggering the cell response and their consequences in determining inflammation onset and resolution.

Study on pedestrian thorax injury in vehicle-to-pedestrian collisions using finite element analysis

Objective： To explore the relationship between the collision parameters of vehicle and the pedestrian thorax injury by establishing the chest simulation models in car-pedestrian collision at different velocities and angles. Methods： 87 cases of vehicle-to-pedestrian accidents, with detailed injury information and determined vehicle impact parameters, were included. The severity of injury was scaled in line with the Abbreviated Injury Scale （AIS）. The chest biomechanical response parameters and change characteristics were obtained by using Hyperworks and LS-DYNA computing. Simulation analysis was applied to compare the characteristics of injuries. Results： When impact velocities at 25, 40 and 55 km/h, respectively, 1） the maximum values of thorax velocity criterion （VC） were for 0.29, 0.83 and 2.58 m/s; and at the same collision velocity, the thorax VC from the impact on pedestrian＇s front was successively greater than on his back and on his side; 2） the maximum values of peak stress on ribs were 154,177 and 209 MPa; and at the same velocity, peak stress values on ribs from the impact on pedestrian＇s side were greater than on his front and his back. Conclusion： There is a positive correlation between the severity and risk of thorax injury and the collision velocity and angle of car-thorax crashes. At the same velocity, it is of greater damage risk when the soft tissue of thorax under a front impact; and there is also a greater risk of ribs fracture under a side impact of the thorax. This result is of vital significance for diagnosis and protection of thorax collision injuries.

Spatiotemporally controlled,aptamers-mediated growth factor release locally manipulates microvasculature formation within engineered tissues

Spatiotemporally controlled growth factor(GF)delivery is crucial for achieving functional vasculature within engineered tissues.However,conventional GF delivery systems show inability to recapitulate the dynamic and heterogeneous nature of developing tissue’s biochemical microenvironment.Herein,an aptamer-based programmable GF delivery platform is described that harnesses dynamic affinity interactions for facilitating spatiotemporal control over vascular endothelial GF(VEGF165)bioavailability within gelatin methacryloyl matrices.The platform showcases localized VEGF165 sequestration from the culture medium(offering spatial-control)and leverages aptamer-complementary sequence(CS)hybridization for triggering VEGF165 release(offering temporal-control),without non-specific leakage.Furthermore,extensive 3D co-culture studies(human umbilical vein-derived endothelial cells&mesenchymal stromal cells),in bi-phasic hydrogel systems revealed its fundamentally novel capability to selectively guide cell responses and manipulate lumen-like microvascular networks via spatiotemporally controlling VEGF165 bioavailability within 3D microenvironment.This platform utilizes CS as an external biochemical trigger for guiding vascular morphogenesis which is suitable for creating dynamically controlled engineered tissues.